1. Field of the Invention
This invention relates to a pointer for measuring instruments, and more particularly to a light-emitting pointer for measuring instruments, which is used in conjunction with the dial plate of a measuring instrument for vehicles such as an automobile to indicate a measured value on the dial plate.
2. Description of the Related Art
Various vehicles such as an automobile and the like are generally installed with measuring instruments for indicating measured values such as velocities of the vehicles, engine torques and the like.
Of these, measuring instruments of analog type include a dial plate with graduations, letters and the like formed thereon, and a pointer that cooperates with such graduations, letters and the like to indicate measured values. In a number of analog instruments, the pointer is so constructed as to be self-illuminated to enable the measured value to be readily recognized even in the darkness.
FIG. 11 is a sectional view showing the construction of an essential portion of a conventional measuring instrument for vehicles with a self-illuminated pointer.
The measuring instrument generally designated at 61 in FIG. 11 includes a casing 63 comprising a printed substrate, a graduations, letters and the like-formed dial plate 65 disposed forwardly of the casing 63, a pointer 67, an internal 69 for rotary driving the pointer 67, sources of light 71 for illuminating the pointer 67, and a light-guiding plate 73 for guiding light from the sources of light 71 to the pointer 67.
The internal drive 69 comprises a main body 69a mounted on the casing 63 and having a coil (not shown) contained therein, and a drive shaft 69b protruding forwards from the main body 69a. The drive shaft 69b is circumferentially rotatably supported in the main body 69a and caused to rotate when the coil in the main body 69a is energized.
Each source of light 71 comprises, for example, an incandescent bulb and is supported on the casing 63 at a position spaced from the main body 69a of the internal drive 69.
The light-guiding plate 73 is formed from a synthetic resin material excellent in light transmission properties, e.g. transparent acrylic resin or the like and comprises light-receiving portions 73a located forwardly of the sources of light 71 and a light-guiding portion 73b extending from the respective light-receiving portions 73a over the main body 69a.
Each light-receiving portion 73a is of substantially hemispherical shape directed towards the source of light 71, a shaft hole 73c is formed at the area of the light-guiding portion 73b in front of the main body 69a, and the drive shaft 69b extends through the shaft hole 73c so that its front end is located forwardly of the light-guiding plate 73.
The light-guiding portion 73b has reflecting surfaces 73d formed at an inclination of substantially 45.degree. at positions close to the light-receiving portions 73a and close to the shaft hole 73c.
The pointer 67, like the light-guiding plate 73, is formed from a synthetic resin material excellent in light transmission properties and comprises a substantially cylindrical fixing portion 67a fitted over the front end of the drive shaft 69b and a long flat indicating portion 67b extending from the fixing portion 67a, in a radial direction of the drive shaft 69b.
At the front of the fixing portion 67a are formed two reflecting surfaces 67c each at an inclination of substantially 45.degree.. At the rear of the fixing portion 67a at a position substantially opposite one of the above reflecting surfaces 67c is formed a reflecting surface 67d at an inclination of substantially 45.degree.. The fixing portion 67a is covered with a light-leakage prevention cap 75.
The rear surface of the indicating portion 67b facing the dial plate is colored, e.g. red with hot melt to prevent leakage of light to the side of the dial plate 65 and to improve the viewability of the indicating portion 67b as the sources of light 71 are turned off.
With the thus constructed conventional measuring instrument 61, the light from the light source 71 falls on the light-receiving portion 73a and into the light-guiding plate 73. The light is subjected to irregular reflections inside the light-guiding plate 73 and reflected at reflecting surfaces 73d to be guided to the area around the shaft hole 73c, and further falls on the rear surface of the fixing portion 67a and into the pointer 67.
The light having entered the pointer 67 is then reflected at reflecting surfaces 67c, 67d to be guided to the indicating portion 67b, wherein the light is irregularly reflected so that the light is emitted forwards from the front surface of the indicating portion 67b to illuminate the pointer 67.
However, the conventional measuring instrument 61, in which light is guided from the light sources 71 to illuminate the pointer 67 has two drawbacks as mentioned below.
First, to guide light from the light sources 71 to the inside of the indicating portion 67b, the light-guiding plate 73 and the pointer 67 must be subjected to complicated processing so that they are provided with shapes such as the reflecting surfaces 67c, 67d, 73d and the like, resulting in the cost increased.
Second, most of the light incident on the rear surface of the fixing portion 67a and into the pointer 67, and reflected at reflecting surfaces 67c, 67d, moves straight inside the pointer 67 to the tip of the indicating portion 67b without being irregularly reflected at the area of the indicating portion 67b closer to the light-guiding plate 73 (the area on the root side of the indicating portion 67b).
Consequently, the indicating portion 67b becomes stronger in brightness at an area of the indicating portion 67b farthest from the leakage prevention cap 75 than at the area of the indicating portion 67b which is closer to the leakage prevention cap 75, making it difficult to illuminate the entire indicating portion 67b with uniform brightness.
Such being the case, in recent years a light-emitting pointer has been proposed in which an electroluminescence element (hereinafter abbreviated as EL element) is used to constitute the indicating portion.
FIG. 12 is a perspective view showing the indicating portion of a heretofore-proposed light-emitting pointer, in which designated at 81 is the indicating portion, 83 a core and 85 an EL element.
The core 83, which is of column shape, is formed from a conductive metal such as decarbonized steel, and the EL element 85 is concentrically formed around the core.
As shown in FIG. 13, a section viewed in the direction of an arrow A in FIG. 12, the EL element 85 includes a circular insulating layer 85a, a fluorescent layer 85b, a transparent electrode film 85c and a light-transmitting, insulating protective layer 85d laminated in sequence around the outer periphery of the core 83 by a method such as dipping, calcination or the like.
The transparent electrode film 85c comprises, for example, an ITO (indium tin oxide) electrode, and in the indicating portion 81, the core 83 serves as one of the electrodes for the EL element 85 corresponding to the transparent electrode film 85c.
The indicating portion 81 is constructed so that, as a voltage is impressed between the core 83 and the transparent electrode film 85c, the fluorescent substance of the fluorescent layer 85b is excited to cause the entire fluorescent layer 85b to emit light at its surface, which light is then transmitted through the insulating protective layer 85d to be emitted outwardly of the indicating portion 81 so that the indicating portion 81 is as a whole illuminated.
The pointer of such construction has an advantage that, since the indicating portion 81 itself has a source of light that emits light at the surface with a uniform distribution of light, i.e., the EL element 85, the indicating portion 81 is entirely evenly illuminated with uniform brightness.
In addition, since in the pointer of such construction the surface of the indicating portion 81, i.e., the surface of the EL element 85 is arcuated circumferentially of the core 83, as compared with the pointer 67 in FIG. 11 having a flat indicating portion 67b that emits light only from its front surface, the indicating portion 81 is three-dimensionally recognized and makes an improvement in appearance and grade as well as in practical utility of the pointer.
With the pointer of the construction as shown in FIGS. 12 and 13, however, since the EL element 85 has an arcuate surface configuration, to laminate each layer of the EL element 85, a method such as dipping, calcination or the like must be employed which is costly as compared with printing commonly used in the formation of a sheet-like EL panel. As a result, it has been impossible to realize a reduction in the cost for the part.